Auto Setup – hints for budding AV ninjas! – Part 2

In our last article we talked about the use of auto setup routines. These can be a godsend in simplifying first time setup but can be fooled by oddities in the room.

So, assuming all went ok with the auto setup routine how can we improve on this by fine-tuning?

This week we’ll look at distance…

Although sound travels much slower than light, the time it takes to reach our ears when arriving from multiple sound sources is still very important. We know from earlier discussions that the same sounds are often emitted from multiple speakers to create the illusion of a sound coming from all around (an explosion in a movie for example). In this case we have to ensure all sounds emitted from the speakers arrive at our ears at the same time or we risk phase cancellation meaning some of the sound disappears.

For a full explanation of phase cancellation take a look at our earlier article on the subject.

So how precise do we need to be with distance settings? In an ideal world we need to be absolutely spot on. This will ensure complete phase accuracy for all arriving sounds. In practice there are limits to what we can achieve though.

A point of reference

Before we start experimenting we need to have a precise point of reference for the listening position. So, get ready to move your chair out of the way for a moment and find a specific point on the ground as your listening reference point. Obviously this should be roughly underneath your head position when listening!

Many AV processors (and AV receivers) allow for setting the distance to the nearest 10cm. In practice this means the error will be one full wavelength at 3400Hz. We know (again from our previous articles) that we hear many sounds above this frequency! In practice we should aim for phase accuracy to the same half wavelength at a frequency much higher than that.

If we can arrange our speakers (and / or delays) so that arriving sounds are in the same half wave (and therefore unlikely to wholly cancel) at a frequency closer to our 20KHz-hearing limit then a more of the sound will remain intact and our listening experience will improve. As it happens arranging speakers to be within 1cm of each other in terms of distance will mean half-wave phase accuracy up to about 17KHz. This is a much more practical target, results in some very useful improvements in sound staging and greatly helps the individual speakers “disappear” and the sound become a cohesive whole.

Better setup routines

In some modern AV processors (including Arcam’s own AVR400/500/600 and AV888) allow for 1cm settings in the setup menus, which saves a lot of fiddling around with speaker positions. If you don’t currently have one of these units why not try moving your speakers as discussed above and see what happens. Or, have a chat to your local dealer and take a listen to one setup this way!

As with all our articles do let us know what you find in your own experiments!